1. Field of the Invention
This invention relates to oil and gas drilling, and more particularly to apparatus and methods for reliably transmitting information along downhole drilling strings.
2. Background
In the downhole drilling industry, MWD and LWD tools are used to take measurements and gather information concerning downhole geological formations, status of downhole tools, and other conditions located downhole. Such data is useful to drill operators, geologists, engineers, and other personnel located at the surface. This data may be used to adjust drilling parameters, such as drilling direction, penetration speed, and the like, to effectively tap into an oil, gas, or other mineral bearing reservoir. Data may be gathered at various points along the drill string, such as from a bottom hole assembly or from sensors distributed along the drill string.
Nevertheless, data gathering and analysis represent only certain aspects of the overall process. Once gathered, apparatus and methods are needed to rapidly and reliably transmit the data to the earth's surface. Traditionally, technologies such as mud pulse telemetry have been used to transmit data to the surface. However, most traditional methods are limited to very slow data rates and are inadequate for transmitting large quantities of data at high speeds.
In order to overcome these limitations, various efforts have been made to transmit data along electrical and other types of cable integrated directly into drill string components, such as sections of drill pipe. In such systems, electrical contacts or other transmission elements are used to transmit data across tool joints or connection points in the drill string. Nevertheless, many of these efforts have been largely abandoned or frustrated due to unreliability and complexity.
For example, one challenge is effectively integrating a transmission line into a downhole tool, such as a section of tool. Due to the inherent nature of drilling, most downhole tools have an elongated cylindrical shape defining a central bore. The wall thickness surrounding the central bore is typically designed in accordance with weight, strength, and other constraints needed to operate in a downhole environment. In some cases, the wall thickness may not be sufficient to allow for direct integration of a transmission line into the wall without significantly weakening the wall. Thus, in certain instances, the transmission line may be routed through the internal bore of the downhole tool.
Nevertheless, routing the transmission line through the internal bore may create interference between the transmission line and drilling fluids, cements, wireline tools, or other substances or objects passing through the central bore. Moreover, in directional drilling applications, drill tools may bend slightly as a drill string deviates from a straight path. In these circumstances, the transmission line may actually deviate away from the internal surface of the central bore, thereby worsening the obstruction within the internal bore of the downhole tool. The operation of drilling fluids, cement, wireline tools, or other components may be adversely affected by interference with the transmission line or, in other instances, the transmission line itself may be damaged.
Thus, what are needed are apparatus and methods to route a transmission line though the central bore of a downhole tool, without interfering with drilling fluids, cement, wireline tools, or other components that may be present in the central bore.
What are further needed are apparatus and methods to keep a transmission line firmly pressed against the inside surface of the central bore even when the downhole tool bends or deviates from a linear path.
What are further needed are apparatus and methods to protect a transmission line from components or substances located or traveling through the central bore of a downhole tool.